This invention relates generally to portable machines for fusing polyolefin pipe and more particularly concerns a self-contained and self-propelled machine and method for the end-to-end treatment of two axially aligned pipe ends for the purpose of heat fusing such pipes together.
The principle of heat fusion is to heat two surfaces to a designated temperature and then fuse them together by application of force. The pressure causes flow of the melted materials, which causes mixing and thus fusion. When the polyolefin pipe is heated, the molecular structure is transformed from a crystalline state into an amorphous condition. When fusion pressure is applied, the molecules from each pipe end mix. As the joint cools, the molecules return to their crystalline form, the original interfaces are gone, and the two pipes have become one homogeneous pipe. The joint area becomes stronger than the pipe itself in both tensile and pressure conditions.
The principle operations of this fusion process include clamping the pipe pieces axially to allow all subsequent operations to take place, facing the pipe ends to establish clean parallel mating surfaces perpendicular to the centerline of the pipes, aligning the pipe ends with each other to minimize mismatch or high-low of the pipe walls, heating at a first specified force in a melt pattern that penetrates into the pipe around both pipe ends, joining the melt patterns with a second specified force which must be constant around the interface area and holding the molten joint immobile with a third specified force until adequately cooled.
Presently known portable pipe fusion machines are typically four wheeled cart type machines such as described in U.S. Pat. No. 3,729,360; No. 4,352,708 and No. 5,013,376. While these machines perform quite well, they require a good deal of labor and additional expensive equipment such as cranes, forklifts, tractors, trucks and the like to load, unload and precisely position the machine on the pipeline. Many machines are damaged during the loading and unloading process. Furthermore, the operators experience stress and fatigue in maneuvering the machines over difficult terrain and conditions.
In addition to the mobility, maneuverability and stability problems of the overall machines, various known machine components also present additional problems. The hydraulic systems are complex and unwieldy and require expenditure of considerable time and labor in preparation for off-cart use. The hydraulics are limited in that they permit selection of only a few operating pressures. The facing operation is complicated because the facer is not easily maneuverable into and out of position between the pipes by one operator when working with the machine off-cart. The facer guide bearings, which are traditionally integral to the body, wear and eventually accuracy in axial registration of the fixed and moving pipes is diminished. This results in undesirable down time of the machine during repair and costly repair to the facer. The jaw assembly necessary to grip and move the pipes during the process requires the front of the cart to be at the free pipe end of the pipe line. The heater is awkward to store for transport and to support on site during periods of non-use.
It is, therefore, an object of this invention to provide a machine, and a method using the machine, for fusing polyolefin pipes which are fully self-contained. Another object of this invention to provide a machine, and a method using the machine, for fusing polyolefin pipes which requires no additional equipment to support operation of the machine. Still another object of this invention to provide a machine, and a method using the machine, for fusing polyolefin pipes which has transport tracks aligned for movement along an axis parallel to the axial pipe alignment within the machine jaws. It is also an object of this invention to provide a machine, and a method using the machine, for fusing polyolefin pipes which is fully self-propelled for forward or reverse movement, left or right movement and pivotal movement about its center. A further object of this invention to provide a machine, and a method using the machine, for fusing polyolefin pipes which is movable along the pipeline from a completed joint to the next joint location. Another object of this invention is to provide a machine, add a method using the machine, for fusing polyolefin pipes which has a tracked undercarriage to increase mobility, stability and maneuverability. Yet another object of this invention is to provide a machine, and a method using the machine, for fusing polyolefin pipes which is easily maneuverable over difficult terrain. It is also an object of this invention to provide a machine, and a method using the machine, for fusing polyolefin pipes which facilitates axial alignment of the machine with the pipeline. A further object of this invention is to provide a machine, and a method using the machine, for fusing polyolefin pipes which has a low center of mass to increase stability. Another object of this invention is to provide a machine, and a method using the machine, for fusing polyolefin pipes which has a jaw assembly easily removed from the machine into remote or in-ditch positions. Yet another object of this invention is to provide a machine, and a method using the machine, for fusing polyolefin pipes which is computer controlled for operation in a variety of modes. Another object of this invention is to provide a machine, and a method using the machine, for fusing polyolefin pipes which is computerized to permit selection of a wide range of operating pressures. Still another object of this invention is to provide a machine, and a method using the machine, for fusing polyolefin pipes which having a facer with wear compensating guide bearings which are easily replaceable in the field.